Crystalline phase discriminating neutron tomography using advanced reconstruction methods

TL;DR

This paper introduces a novel iterative reconstruction method for high-resolution Bragg edge neutron tomography that outperforms traditional techniques, enabling detailed phase discrimination with less exposure time.

Contribution

A new regularisation-based iterative reconstruction approach tailored for spectral and spatial dimensions in neutron tomography is proposed, improving phase identification accuracy.

Findings

Outperforms FBP and existing regularisers in multi-material phantom reconstructions.

Requires significantly less neutron exposure time for high-quality results.

Enables voxel-level crystallographic phase identification.

Abstract

Time-of-flight neutron imaging offers complementary attenuation contrast to X-ray computed tomography (CT), coupled with the ability to extract additional information from the variation in attenuation as a function of neutron energy (time of flight) at every point (voxel) in the image. In particular Bragg edge positions provide crystallographic information and therefore enable the identification of crystalline phases directly. Here we demonstrate Bragg edge tomography with high spatial and spectral resolution. We propose a new iterative tomographic reconstruction method with a tailored regularisation term to achieve high quality reconstruction from low-count data, where conventional filtered back-projection (FBP) fails. The regularisation acts in a separated mode for spatial and spectral dimensions and favours characteristic piece-wise constant and piece-wise smooth behaviour in the respective dimensions. The proposed method is compared against FBP and a state-of-the-art regulariser for multi-channel tomography on a multi-material phantom. The proposed new regulariser which accommodates specific image properties outperforms both conventional and state-of-the-art methods and therefore facilitates Bragg edge fitting at the voxel level. The proposed method requires significantly shorter exposure to retrieve features of interest. This in turn facilitates more efficient usage of expensive neutron beamline time and enables the full utilisation of state-of-the-art high resolution detectors.